1. The Field of the Invention
This invention relates to spinal vertebral implants and methods and instruments for inserting the implants between spinal vertebrae in order to achieve spinal fusion.
2. The Prior State of the Art
When tissues between spinal vertebrae, also known as intervertebral disks, become herniated or otherwise injured, the disks can compress against nerves associated with a particular location on a spinal column. Such injuries are common in the lumbar vertebrae, for example, and can cause extreme pain to a patient suffering from such injuries.
One treatment common among medical providers to treat such injured intervertebral disks is a spinal fusion. In typical spinal fusion procedures, a portion of a vertebral disk or the entire vertebral disk is removed from between adjacent upper and lower vertebrae and the upper and lower vertebrae are fused to form a single spinal structure. The fusion of the vertebrae can alleviate the pain and discomfort associated with injured disks and frequently does not result in significant loss of bending capability.
A variety of different treatment modalities have been developed to perform such spinal fusions. Examples of typical treatments include the use of a spinal implant placed between two adjacent vertebrae. Typical implants include those made from bone, often harvested from a cadaver, for example. Following the removal of the intervertebral disk, the spinal implant is placed between the vertebrae and fuses over time with the vertebrae, eventually forming a single fused member. Typical implants can also comprise a metallic material, for example.
A variety of different approaches have been developed to use implants to achieve spinal fusion. For example, one approach employs a cage-like metallic structure in which fragments of bone are placed. The cage is mounted between adjacent vertebrae and is designed to maintain distraction between vertebrae, thus maintaining the vertebrae a desired distance apart from each other. The bone fragments foster fusion between the adjacent vertebrae. However, the cage-like structures merely act as distractors and do not fuse between the vertebrae. Instead, only the bone fragments foster fusion between the vertebrae. Thus, the space used by the cage is not used to foster bone growth and fusion. Furthermore, if bone growth does not occur through the holes for any reason, the implants merely serve as distractors, that is, placeholders that maintain spaces between adjacent vertebrae, rather then fostering fusion therebetween. The use of metal cages also introduces a foreign object into the disk space where fusion is to be obtained.
Other implants comprise harvested bone without a cage member. Typical such implants include implants comprising first and second bone pieces coupled together, for example. However, such coupled pieces can fail to fuse to each other, or can form a false joint which can eventually result in decreased fusion or the lack thereof.
There is therefore a need in the art for an improved spinal fusion implant that can be mounted between adjacent vertebrae and achieve fusion therebetween. There is also a need in the art for an improved method for placing spinal fusion implants between adjacent vertebrae. There is also a need in the art for instruments capable of achieving improved methods for implanting spinal implants.
The present invention relates to a spinal vertebral implant comprising a substantially rectangular shaped base section comprising a solid piece of bone. A nose section extends integrally from the substantially rectangularly shaped base section and preferably has a tapering shape to foster entry between adjacent vertebrae. The distal tip of the implant can be pointed or rounded, for example. The preferred nose section tapers distally and inwardly from the base section to form the distal tip portion and comprises a solid piece of bone. The implant is preferably cut from a longitudinal section of a long bone of a human cadaver.
Serrated sides assist the implant in gripping adjacent upper and lower vertebrae and in being maintained therebetween. The serrations are preferably angled in a manner that encourages the implant to be maintained between the adjacent vertebrae upon placement therebetween. The serrations grip and can impact into the adjacent vertebrae. Thus, the serrations assist in maintaining the implant tightly within the intervertebral space. First and second implants are generally placed into respective left and right sides of an intervertebral space unless the patient suffers from scoliosis or another particular condition or treatment modality applies, in which case it may be possible to use only one implant. In yet another embodiment, more than two implants are implanted, however, at least two implants are generally preferred.
A method for placing one or more implants between the adjacent vertebrae comprises forming one or more angled slots located in posterior portions of the vertebrae and configured to receive an implant. The implant is inserted into the angled slot and then further inserted between the vertebrae. Each slot is preferably formed from an upper slot portion and a lower slot portion in the respective upper and lower vertebrae. Each of these slot portions may be formed in a variety of different manners, such as by cutting or crushing a posterior portion of the edge of adjacent vertebrae. Once the implant is initially inserted into the slot, the implant can be pressed further between the vertebrae, thereby forcing a tightly inserted fit between the implant and the adjacent vertebrae.
In one embodiment, one or more slots extend from the posterior ends of the vertebrae at least approximately one third to approximately one half the distance between the anterior and posterior ends of the upper and lower vertebrae, although a variety of different configurations are available.
In one embodiment, each of the upper and lower slot portions are angled with respect to the longitudinal axis of the upper and lower vertebrae such that the placement of rectangular implants within the slots and the subsequent compression of the posterior portions of the vertebrae results in a desired level of lordosis. Through the use of the angled slots and a rectangular piece of bone, the anterior portions of the vertebrae are distracted or spread apart, thereby producing lordosis.
Instruments specifically designed to assist in the formation and ultimate configuration of the slots include, for example, (i) osteotomes designed to form a slot having a size substantially corresponding to the implant; (ii) an impactor designed to substantially mate with the proximal portion of the implant and drive the implant between adjacent vertebrae; (iii) and spacers having varying sizes that are designed to assist in enlarging the space between adjacent vertebrae and provide a space for the implant. Optionally, other instruments are employed to crush the cortical posterior bone portions. These and/or other instruments and one or more implants may form a kit for filling an intervertebral space with materials enabling fusion of upper and lower vertebrae. Other components of the kit may include bone fragments to be placed in the slots and the remaining portion of the intervertebral space to completely fill in the intervertebral space. Mechanical fixation devices such as pedicle screws and related instruments may also be used to secure the vertebrae in place and apply compression to the posterior region following the placement of the implant between adjacent vertebrae, thereby achieving and maintaining a desired level of lordosis.
The preferred longitudinally cut implant can be contacted by an instrument such as an implant impactor with significant force at a posterior end of the implant without splitting or crushing the implant. This is in part because the direction of the impact from the implant impactor is in a linear relationship with the orientation of the grain of the bone forming the implant, rather than perpendicular to the grain of the bone forming the implant.
Also in light of the use of the cut slots, the implanted implant and associated bone fragments become incorporated more readily into the spine as part of the fusion for two reasons. First, the slots offer increased surface area. Second, the cutting of the slots causes the bone to more readily fuse.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.